Revert "Revert "Change default settings for automount""

This reverts commit 96231d0c

As already outlined in 96231d0c (comment 152483) I (at least partly) disagree with the reasoning that was given in the revert commit description.

There has been some additional discussion (on Nate's blog) suggesting to fix not working bookmarks in Dolphin on non mounted drives (and I just created a bug for that: https://bugs.kde.org/show_bug.cgi?id=430557), but there are still other cases where this doesn't help, at least I experienced that on Manjaro.

Additionally I don't think the brought up downsides justify the revert:

• security - I now know of one bug GNOME had in combination with file indexing. From what I know it only took to plug in a USB drive with images to unlock a locked session.
• problems with multiple users - user B cannot access a drive (like an USB stick) that was plugged in (and thus automounted) from user A) - this is the same as if user A manually mounts the drive, but I agree that the likelihood for this to happen is much higher with automount.